1. Field of Invention
This invention relates to a timer mechanism and, in particular, to a timer mechanism useful for controlling set-back intervals of preselected control temperatures for the thermostat.
2. Brief Description of the Prior Art
Space heating thermostats such as the typical wall mounted thermostats used in rooms of buildings have, in recent years, been provided with set-back capability. An example of a thermostat of this nature is that shown in U.S. Pat. No. 3,948,441 which includes a battery driven clock mechanism which is functional to change the preselected control temperature between preselected control temperatures at preselected periods during a day.
One of the difficulties associated with the aforementioned timer control thermostat is that many applications require multiple set-backs of the control temperature. As, for example, a working couple are away from their dwelling for extended daytime periods. The thermostat for this application desirably should provide for the automatic set-back of the control temperature during night hours when the occupants are asleep and also during day hours when the occupants are at work.
The timer mechanisms typically have 24-hour dials so that the set-back point can be selected once in every twenty-four period. It is desirable in such a mechanism to provide the capability for yet another set-back period and further desirable that such set-back period can be cancelled so that a single thermostat model can be employed, interchangeably, for single and dual set-back periods.